This invention relates to processes for extraction of aromatic compounds from nonaromatic compounds by means of selective solvents for aromatic compounds, and more particularly to a novel method of controlling corrosion in the solvent recovery systems of such processes.
In such processes, the principal products of the extraction step are a solvent phase containing principally solvent and extracted aromatic compounds and a raffinate phase containing principally unextracted nonaromatic compounds. The solvent phase is customarily distilled to separate a product containing principally solvent from a product, the extract, containing principally aromatic compounds. The solvent is recycled to the extraction step for reuse in the extraction process.
Frequently, in such process systems, acidic products are generated as a result of oxidation of the solvent. For example, in one system using triethylene glycol as the solvent, it has been found that the rate of formation of proton (H.sup.+) in the solvent, at 150.degree. C. in the presence of air is 1.921.times.10.sup.-7 mole per liter per 33 hours. In the same period, the pH of the process water in the system dropped from 8.10 to 6.63. Acids generated by solvent decomposition have caused corrosion problems in of the process systems. The major contaminants in the solvent and in the water system have been found to be iron-containing particulates, apparently from corrosion of process equipment caused by the acidic contaminants.